The present invention generally refers to padded elements used in motor-vehicles, comprising a padding body, usually made of foamed plastic material, and a cover applied thereon. The invention particularly relates to a method and apparatus for manufacture of a padded element, particularly for a motor-vehicle seat, of the type wherein a cover is applied onto a padding body and the cover is formed according to the shape of the surface of the padding by pressing in a mold and simultaneous application of a flow of steam. The invention however applies also to other padded elements used in motor-vehicles, such as door panels, roof panels, and dashboard panels.
By the term "padded element" of a motor-vehicle seat, reference is made in the present description and in the following claims either to the seat portion or the backrest portion of the seat. This element is formed by a padding body, usually made of foamed plastic material, on which there is applied a cover (made of fabric, skin, or synthetic material) which may be provided on its back with a relatively thin and soft layer of foamed plastic material.
According to the most conventional technique, the padding body of the seat element is covered with a fabric which is secured to the body of foamed plastic material by sewing or by means of an adhesive material or by fixing elements which connect the cover to the body of foamed plastic material. These last two techniques have the advantage, with respect to the most conventional technique which provides the sewing of the cover, to be more adapted to mass production and to allow in particular the manufacturing process to be automated, while enabling the production of complex anatomical shapes, which answer to ergonomic and comfort needs. On the other hand, said know processes imply the risk, following the connection of the covering fabric to the surface of the padding element, that the fabric is torn, if it is not elastic.
In order to solve this problem, it has been proposed to use a thermo-formable material for covering the padding of foamed plastic material. This fabric is initially heated and then formed according to the desired shape by cold pressing in a mold. The fabric formed thereby is then connected to the body of foamed plastic material. This known method however has the drawback of requiring the use of a thermo-formable fabric, which is of a relatively high cost, and to prevent the use of fabrics having decorative designs, since such designs are deformed in the thermo-forming operation.
A solution to the problem of providing a cushion with a complex shape while adopting a regular non-elastic fabric as a cover, and avoiding the risk of tears and/or lacerations of the fabric when it is coupled to the padding, lies in forming the covering fabric, before application thereof to the padding, by a heat pressing operation with application of steam. A method of this type is disclosed in FR-A-2,347,306. If on one hand the simple idea of imparting a determined shape to an non-elastic fabric by heat pressing with steam is surely an obvious step for a skilled man in the art of fabric forming, given that it is the conventional method used, also at home, when forming fabrics of clothes, as well as covering fabrics in general, on the other hand, it must be pointed out that the practical application on an industrial scale of this idea is not absolutely easy. Various tests have shown indeed that the above mentioned method, as it is described in FR-A-2,347,306, cannot be used practically in the industry, since it implies a high risk that the steam which is applied during the pressing of the fabric tends at least partially to condense on the fabric itself, giving origin to stains.
The above mentioned problem has been overcome with the method and apparatus forming the subject of Italian patent application No. 67757-A/86 of Oct. 6, 1986 and in the corresponding U.S. Pat. No. 4,844,761. According to this solution, the cover is initially applied to a lower mold which is provided with an apparatus for injecting steam on the cover during pressing. The steam is caused to come to passages formed in the lower mold by being taken from a reservoir of steam under pressure which is remote with respect to said passages and whose body is however able to transfer heat by thermal conduction and by radiation to the wall of the lower mold. In this way, the risk of dew formation and resulting stains on the fabric is reduced at minimum, since the wall of the lower mold is kept efficiently and constantly at high temperature, due to the heat transmission from the body of the steam reservoir to said upper wall. At the same time, a prolonged contact of the steam with the fabric is avoided, since the pressure chamber of the steam reservoir is not in direct communication with the passages formed in said upper wall. After the covering fabric is formed, the latter is applied to the padding of foamed plastic material by glueing with the aid of an adhesive.
Tests have shown that this last known method is very good in order to solve the technical problems which have been disclosed above. However it is not completely satisfactory from the point of view of economy of manufacture, when an automated mass-production is to be prepared. Indeed, when the above described method is to be carried out in a production line, it is necessary to provide, for each padding body to be covered, a relatively complicated lower mold equipment, provided with said devices for injecting steam and the associated reservoir of steam under pressure, which causes very high investments and does not provide for flexibility of production. A further drawback of the method disclosed in U.S. Pat. No. 4,844,761 lies in that it does not allow the use of sheets of adhesive material of the so called "hot-melt" type, in lieu of the conventional adhesive for glueing the cover on the padding body. These sheets must be interposed between the parts to be glued and melt when a predetermined temperature is passed so as to provide glueing. The advantage thereof lies in that they provide a "reversible" glueing, i.e. they allow at a later stage unglueing of the cover by application of heat. With said known device, the heated steam injection stage is provided during pressing the cover between two molds, without the padding body being present. Therefore, if a "hot-melt" sheet is applied to the cover at this stage, it would melt over the metal mold which is pressed thereagainst. Therefore, it would be necessary to provide an additional operation for applying the "hot-melt" sheet, following the stage of steam application.
Finally, a further drawback of the method forming the subject of the above identified Italian patent application lies in that it must be necessarily divided in two stages, i.e. a first stage in which the sole cover is formed by heat pressing with injection of steam and a second stage in which the padding body is glued on the previously formed cover.